Apparatus for purification of exhaust gas and method for purification of exhaust gas using the same

Abstract

An apparatus for purification of exhaust gas comprises: an exhaust gas pipe ( 2 ) connected to an internal combustion engine ( 1 ); an upstream catalyst ( 3 ) arranged at the upstream side of an exhaust gas passage inside the exhaust gas pipe ( 2 ); a downstream catalyst ( 4 ) which is arranged at the downstream side of the exhaust gas passage inside the exhaust gas pipe ( 2 ), and on which nickel and/or iron is supported; and oxidizing gas supply means ( 5 ) which is connected to the exhaust gas pipe ( 2 ) between the upstream catalyst ( 3 ) and the downstream catalyst ( 4 ), and which supplies oxidizing gas into the exhaust gas pipe ( 2 ).

1 . An apparatus for purification of exhaust gas, comprising:
 an exhaust gas pipe connected to an internal combustion engine;   an upstream catalyst arranged at the upstream side of an exhaust gas passage inside the exhaust gas pipe;   a downstream catalyst which is arranged at the downstream side of the exhaust gas passage inside the exhaust gas pipe, and on which nickel and/or iron is supported; and   oxidizing gas supply means which is connected to the exhaust gas pipe between the upstream catalyst and the downstream catalyst, and which supplies oxidizing gas into the exhaust gas pipe.   
   
   
       2 . The apparatus for purification of exhaust gas according to  claim 1 , further comprising control means, wherein, when it is determined that the downstream catalyst has a bed temperature ranging from 400° C. to 750° C., and that an air-fuel ratio of exhaust gas flowing into the downstream catalyst is in a rich state, said control means controls the air-fuel ratio to become in any one of a lean state and a stoichiometric state by temporarily supplying the oxidizing gas from the oxidizing gas supply means. 
   
   
       3 . The apparatus for purification of exhaust gas according to  claim 2 , wherein
 the internal combustion engine is an engine for an automobile, and   when the downstream catalyst has a bed temperature ranging from 400° C. to 750° C., when the air-fuel ratio of exhaust gas flowing into the downstream catalyst is in a rich state, and in any one of cases where a speed of the automobile is 10 Km/h or below and where a number of engine revolutions is 1000 rpm or below, the control means controls the air-fuel ratio to become in any one of a lean state and a stoichiometric state by temporarily supplying the oxidizing gas from the oxidizing gas supply means.   
   
   
       4 . A method for purification of exhaust gas emitted from an internal combustion engine using an apparatus for purification of exhaust gas, said apparatus comprising:
 an exhaust gas pipe connected to an internal combustion engine;   an upstream catalyst arranged at the upstream side of an exhaust gas passage inside the exhaust gas pipe;   a downstream catalyst which is arranged at the downstream side of the exhaust gas passage inside the exhaust gas pipe, and on which nickel and/or iron is supported; and   oxidizing gas supply means which is connected to the exhaust gas pipe between the upstream catalyst and the downstream catalyst, and which supplies oxidizing gas into the exhaust gas pipe.   
   
   
       5 . The method for purification of exhaust gas according to  claim 4 , wherein, when it is determined that the downstream catalyst has a bed temperature ranging from 400° C. to 750° C., and that an air-fuel ratio of exhaust gas flowing into the downstream catalyst is in a rich state, the air-fuel ratio is controlled to become in any one of a lean state and a stoichiometric state by temporarily supplying the oxidizing gas from the oxidizing gas supply means. 
   
   
       6 . The method for purification of exhaust gas according to  claim 4 , wherein
 the internal combustion engine is an engine for an automobile, and   when the downstream catalyst has a bed temperature ranging from 400° C. to 750° C., when the air-fuel ratio of exhaust gas flowing into the downstream catalyst is in a rich state, and in any one of cases where a speed of the automobile is 10 Km/h or below and where a number of engine revolutions is 1000 rpm or below, the air-fuel ratio is controlled to become in any one of a lean state and a stoichiometric state by temporarily supplying the oxidizing gas from the oxidizing gas supply means.